1. Field of the Invention
The present invention relates to polydiorganosiloxane-based antifoam compositions and to their use in the reduction of foaming in aqueous liquids.
2. Description of the Prior Art
U.S. Pat. No. 4,076,648 discloses self-dispersible antifoam compositions. The self-dispersible antifoam compositions of said patent comprise a lipophilic nonionic surface active agent, which may be a siloxane-oxyalkylene block copolymer, homogeneously dispersed in a non-emulsified diorganosiloxane antiform agent, which may consist of a finely divided inorganic filler in a diorganopolysiloxane oil. All of the antifoam compositions specifically disclosed by said patent are based upon a polydiorganosiloxane oil having a 25.degree. C. viscosity of 500 centistokes. Said patent teaches, in its generic descriptions, that polydiorganosiloxane oils having 25.degree. C. viscosities of from 5 to 3000 centistokes are preferred and that such oils having viscosities of up to 100,000 may be utilized. Since apparently only the 500 centistoke oil was actually tested, the implication seems to be that the polydiorganosiloxane oil viscosity is not a significant factor, and that such oils having higher viscosities, e.g. up to 100,000 centistokes, would provide antifoam compositions more or less equivalent in effect to those based on the 500 centistoke oil.